


de.riv.a.tive

by meretricula



Category: Bleach, Doctor Who (2005), Iron Man (Movies), Pushing Daisies, Tennis no Oujisama | Prince of Tennis, X-Men (Movies)
Genre: Crossover, F/M, M/M
Language: English
Status: Completed
Published: 2011-10-05
Updated: 2011-10-05
Packaged: 2017-10-24 08:12:57
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 4,179
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/261075
Author URL: https://archiveofourown.org/users/meretricula/pseuds/meretricula
Summary: <blockquote class="userstuff">
              <p>For the paliphrase challenge on Livejournal: a series of four independent ficlets based on the word "derivative". (Prince of Tennis, Bleach Fashion AU, Pushing Daisies/X-Men, Iron Man/Doctor Who)</p>
            </blockquote>





	1. Chapter 1

**Summary for the Chapter:**

> definition 6. Also called differential quotient; especially British, differential coefficient. Mathematics. the limit of the ratio of the increment of a function to the increment of a variable in it, as the latter tends to 0; the instantaneous change of one quantity with respect to another, as velocity, which is the instantaneous change of distance with respect to time. Compare first derivative, second derivative.

"Um, senpai?" Kaidoh hovered in the doorway to the chemistry lab, staring awkwardly at his feet. Inui blinked, carefully set down the beaker of bubbling poison-green liquid he was examining, and removed his goggles.

"How can I help you, Kaidoh?"

Kaidoh fixed his gaze even more intently on his scuffed-up sneakers. He needed to go shoe-shopping soon. "You said, if I ever had trouble with my math homework..."

"Of course!" Inui beamed behind his improbably opaque glasses. "And I have just the thing - Inui Juice Super Special Calculus Remix!"

Kaidoh's head shot up, and the faint blush lingering on his cheeks quickly faded to white, and then continued straight to pale green. "Ah, no, senpai, that's okay," he said hurriedly, preparing to flee.

"Joke, Kaidoh. It was a joke." Inui pretended not to notice how Kaidoh sagged against the doorframe in relief. His juices were very effective! He didn't understand why only Fuji ever wanted to try them. "What topic are you covering in calculus?"

"Integration." Kaidoh stepped into the lab hesitantly, aware that he was entering a dangerous domain. "I didn't do well on the last test."

"Well, why don't you show it to me, and we can see where you went wrong," Inui said cheerfully as he cleared a space on the lab bench. Kaidoh dug in his bag for a moment and produced a sheet of paper, liberally covered with markings in red ink. Inui took it and frowned. "Kaidoh, I know math is not your strongest subject, but thirty-one out of a hundred is..."

"The teacher said I could make it up tomorrow," Kaidoh said, going red again. "So I need to study."

"All right." Inui glanced at the glaring red **31** one last time, then shook his head and returned his attention to Kaidoh. "So what about integration is giving you trouble? I know you understand derivatives just fine."

"I wasn't really paying attention when the teacher introduced this unit, senpai," Kaidoh said humbly. "Maybe you could just explain the whole thing?"

"Well, a derivative is the slope of a line, right? And an integral is the area under it. So if you take the integral of a derivative, you should come back to the original function, the line. So you're trying to see what the function you have is the derivative of. Let's start with a simple function, 3x^2..." Kaidoh's eyes glazed over, and he settled down at the workbench, resting his chin in his hand as he listened to Inui's voice without paying the slightest bit of attention to what he was saying.

Inui frowned, taking in Kaidoh's rapt inattention, and decided to test a theory.

"...so then you multiply everything through by three, factor the polynomial and take the second derivative of the remainder. Why don't you give it a try?"

Kaidoh blinked away his blank stare, took the example Inui had blatantly failed to do anything mathematically feasible to, and integrated it perfectly. Inui looked at the test again, and noticed that every single problem had been integrated properly. Kaidoh had then filled in all the constants - wrong. Then Inui reflected back on the past week, which he had spent cooped up in the chemistry lab trying to refine a new Inui Juice Remix, and considered the possibility that Kaidoh was maybe a little justified in using trickery to get his attention. When he really thought about it, it was pretty flattering - Inui didn't know that he would have sabotaged his own calculus grade for anything or anyone.

"Well, you seem to have a better grip on the concept now," Inui said diplomatically.

"Yes, thank you, senpai," Kaidoh agreed politely, eyes wide and guileless. "You explain things much better than Homura-sensei."

This was actually true in a general sense, Homura-sensei being a mathematical genius but completely incapable of basic human communication, so Inui let it pass. "Would you like to go for a run when you finish your studying?"

"Yes," Kaidoh replied instantly, and went dull red. Inui smiled at him reassuringly (or as reassuringly as Inui could, given that all of his expressions ended up looking threatening; Kaidoh understood the sentiment, at least) and started putting away his chemistry equipment. _Doubles partner > chemistry experiments,_ Inui decided. It was one mathematical expression he should have no difficulty remembering.


	2. Chapter 2

**Summary for the Chapter:**

> de.riv'.a.tive\, n. 1. That which is derived; anything obtained or deduced from another

**Notes for the Chapter:**

> this is part of my sporadically updated Bleach fashion AU, wherein Ichigo is a med student and part-time model and Ishida is a manic fashion designer. previous parts of this universe are [The Devil Wears Square-Rimmed Glasses](http://meretricula.livejournal.com/49939.html) and [The Art of Alliteration](http://meretricula.livejournal.com/57273.html).

"So, Ishida-san, you have a new fashion line coming out! You must be so excited!" The reporter, Inoue-san, was practically bubbling over with excitement herself. Ishida adjusted his glasses.

"I am pleased with the look of my designs," he allowed after a moment's deliberation. "Whether the general public will agree remains to be seen."

"Oh, such a popular designer like you has nothing to worry about," Inoue enthused. "But you always seem to have such wonderfully different ideas behind all the lines that Quincy brand produces. There was the Cross line, with the traditionally inspired look, and Needles & Thread, for the practical-minded housewife, and now Strawberry, for the fashion-forward twenty-something! Tell me, what was your inspiration for your latest line?"

"Oi, Ishida-san," interrupted a young man with brilliantly bleached hair as he barged into the room, "did you steal my clothes again?"

"They are in their usual closet in the modeling room," Ishida sniffed, "not that I can understand why you insist on wearing clothing by such inferior designers. They've been folded, which is probably why you didn't recognize them. Now please leave. As you can see, I am giving an interview."

"Oh, no, of course he can stay!" Inoue said. "I'm Inoue Orihime, from Fashion Japan! Magazine - what's your name?"

"Kurosaki Ichigo." He ducked his head, embarrassed. "I model part-time for Ishida-san, through Senbonzakura Agency."

"Oh, _Ichigo_ ," Inoue said, with a knowing smile. "I suppose you and Ishida-san are very close, then!"

"I wouldn't say _that_ ," Ichido and Ishida said in unison. "I mean, I just wear the clothes he makes when he tells me to," Ichigo went on. "We don't hang out or anything. I probably can't tell you any more than you already know, and I wouldn't know high fashion from a burlap bag, so..."

"I'm sure you're just being modest," Inoue giggled. "After all, you're Ishida-san's mysterious exclusive model! He's very particular about who he allows to model his clothes."

"Uh, okay?" Ichigo just looked confused. "Hey, Ishida-san, while I'm here, I wanted to ask if you could find a replacement model for the Osaka show. I've got a med school exam the next morning."

"So reschedule it," Ishida suggested, through gritted teeth.

"Look, I can't exactly tell them, sorry, I can't come to one of my final exams, I have to model for a _fashion show_ ," Ichigo said, annoyed.

"Then we will reschedule the show," Ishida replied, very precisely. "Give Kuchiki Rukia-san your schedule for the upcoming two weeks, and we will find a solution that works for everyone."

"...all right," Kurosaki said. "But wouldn't it be easier to just get another model?"

" _You_ are my model," Ishida snapped. "Why would I get another one?"

Inoue beamed and watched them bicker, already composing the end of her interview in her head.

 _...and as I watched Ishida-san reschedule an entire fashion show so Kurosaki Ichigo-san could model for it, all I could think was **I hope the Strawberry fashion line lasts a very long time!**_


	3. Chapter 3

**Summary for the Chapter:**

> de.riv.a.tive: (Chem.) A substance so related to another substance by modification or partial substitution as to be regarded as derived from it

Logan had cased the joint before he even sat down. Only one exit, which he had insisted on facing; one door to the kitchen behind the counter, which he could also keep an eye on from where he was sitting. The scattering of customers, despite the early hour, lent the place an air of normality, as did the obnoxiously bubbly blond waitress. It was not Logan's usual type of hangout. "Olive Snooks" (whatever the hell kind of name that was) wouldn't even let him smoke or bring him a beer, and she hadn't looked in the least intimidated when he snarled at her.

However, he reflected with well-concealed resignation, it _was_ the sort of place an ordinary teenager might like, and Marie was already plowing through her third slice of pie, looking happier than she had in months. Ever since her powers had started coming back, she'd retreated more and more behind layers of clothing and sullen silence, and she hadn't left the mansion at all. So Logan had taken the mission, humiliating as it was, to track down a potential mutant pie-maker, solely in order to get her out of the house. He thought it was a pretty damn cunning plan.

"This is the best pie ever," she enthused. "Want a bite?"

"No," Logan grumbled. "I thought the last pie was the best pie ever."

"They're all the best pie ever," Marie said, eyes shining. "Open your mouth."

"I said _no_ ," Logan started, only to be interrupted by a forkful of cherry pie. The ensuing noises he made could have been interpreted as indignation, he thought, soothing his dignity. Even if they had been pure bliss. Marie was right; it was the best pie ever.

"Can I get you anything else?" Olive Snooks, the blond harpy of a waitress, descended upon them with the creepy smile of a used car salesman who knows that all his advertising statements are actually true and, moreover, his products are addictive. "More coffee? More pie?"

"We'd like to speak with the pie-maker," Logan said, pre-empting the request he just knew Marie was about to make. He didn't mind spoiling her a little - Christ knew nobody else was doing it - but he was pretty sure that four slices of pie for breakfast would earn him _words_ from Ororo when they got home.

"Well, I'm afraid he's a bit busy in the kitchen at the moment," Olive apologized, not sounding the least bit sorry. "But I can get you whatever pie you'd like without bothering him."

"It's about a _special_ pie," Marie said, smiling sweetly and pouring on the Southern drawl like syrup. Logan kicked her under the table, but she ignored him. "For our wedding."

"Oh, isn't that just darling!" Olive cooed to Marie, shooting Logan a glare that shouted, _Child molester_. "You stay right there, and I'll see if he can spare a moment to come out and talk with you." She flounced off.

" _Wedding_?" Logan hissed to Marie as soon as she was out of ear-shot. "Have you lost your mind?"

" _I_ didn't invent our cover," she said smugly. "Didn't you read our mission assignment? And anyway, it worked."

Logan scowled, but there wasn't much of an argument to be made when in fact it _had_ worked, so he drank his coffee in grumpy silence.

The pie-maker, when he stumbled out of the kitchen with Olive on his heels like a particularly yappy little dog, didn't look like anybody's idea of a mutant necromancer. He was tall and awkward and wholesomely good-looking, in a nervous sort of way. Logan disliked him on principle. He could hear Marie sighing a little across the table.

"Um, hi, I'm Ned, this is my pie-shop, and Olive said you wanted a pie, in which case you came to the right place, I mean, obviously, it's called the Pie Hole and also you've been eating pie, I did think the cherry turned out pretty well today, though I recommend the blackberry especially, Chuck said it was really good, and Olive did too, but she says that about all my pies so I don't know if that counts for much. Um. Hi?"

"Hi, I'm Marie," Marie said, smiling. She had such a terrible and misplaced soft spot for the socially maladjusted. "This is Logan. We were hoping we could talk to you about making a pie for our wedding."

"You're getting married? That's wonderful! Congratulations!" They all glanced back at the kitchen door, where a brunette in a brightly colored dress was standing. There was a white hand-print at the curve of her waist - flour. "I'll just bring you some more pie," she added, beaming. Logan almost explained that Marie had already had three slices that morning and he didn't care for sweets, but his "bride" kicked him very hard in the shin and glared, and by the time he was done promising retribution using nothing but the subtle movement of his eyebrows, the dark-haired woman was placing two plates of pie on the table. Also, well. It was pretty much the best pie ever.

While Marie was digging into her slice of peach pie, Logan gave the newcomer a once-over. She was standing just barely out of reach of Ned the pie-maker, both of them awkwardly gravitating towards each other and away again. Logan didn't really need his nose to tell him that they were in love, though it did tell him that (as well as the fact that the girl raised bees and liked strawberry-scented shower gel). The Professor had nearly died of scientific curiosity when Logan mentioned that he could smell love, but it really wasn't all that complicated or interesting. Just pheromones, and an increased tendency towards nervous sweat. He could smell that Olive Snook was in love with the pie-maker, too, or at least thought she was, and that Ned the pie-maker had yet to seal the deed with his girl, though she was obviously open to the idea if he was leaving flour-prints on her dresses.

"Oh!" Ned the pie-maker said, belatedly. "This is Chuck, my. Uh. Girlfriend."

Chuck beamed; behind their backs, Olive glared.

"Great," Logan assured him. "Hey, look, can I talk to you in private? It's just that, uh, I want it to be a surprise for my little angel here," he added, gritting his teeth.

"Yeah, um, come on back, we can talk in the kitchen," Ned stammered.

"We'll just stay here and talk about girl things!" Chuck said cheerfully, taking Logan's seat across from Marie. "Olive, come sit with us!"

Well, that took care of the waitress-slash-Pomeranian, at least. Logan followed Ned into the kitchen and cornered him by the sink. "I know what you are," he said bluntly.

"A... pie-maker?" Ned asked, bewildered.

"Besides that. You're a mutant. You bring people back from the dead."

The pie-maker looked at Logan's expression and decided not to bother with denial. "Not really. They have to die again sixty seconds later. I can't bring them back a second time."

Logan blinked. "That's a pretty shitty power, kid."

"I know." Ned glanced down at his hands, which were in gloves just in case he brushed up against Chuck. "Believe me, I know."

"Okay, I'm supposed to tell you that you're not alone, there's help out there for people like you, if you need anything call the number on the card I'm leaving on your counter, but you're old enough to take care of yourself and you seem to be doing okay, so I'm going to take Marie and head on home."

"So you really are getting married?" Ned asked, strangely hopeful.

"Naw. She's, you know. Like us. She can't touch anybody, skin-to-skin."

The pie-maker smiled at Logan, ever so slightly. "Well, there's always a workaround." He turned back to his pies, adding over his shoulder, "Tell Olive I'm giving you a pie, on the house. Whichever one Marie wants."

"Thanks," Logan said, and went back out to collect Marie. He was pretty sure that Ned hadn't told him the whole story, but he frankly didn't care all that much. He'd identified the mutant and gotten Marie out of the house, so as far as he was concerned, his mission was a success. Ned probably knew what he was doing.

Olive had gotten up to serve the customers, so it was just Chuck and Marie, gossiping over half-finished slices of pie. They made a weird if pretty picture, two girls in gloves and scarves, covered up as much as feasible, despite the warm temperature indoors. "C'mon, Marie, pick a pie and we're going."

"Blackberry," Marie decided, smiling at Chuck. The older woman got up to box up their pie behind the counter.

"Here you go," she announced, tying a ribbon around the box. "Compliments of the Pie Hole."

"Thank you," Marie replied, and started to struggle with her coat. Logan sighed and held out the sleeve for her, settling it on her shoulders when she finally got it on. As she picked up the pie, they both caught sight of Ned and Chuck in the kitchen. They were kissing, but there was something funny about the way Chuck was holding her hands up, and Logan realized that she was holding a sheet of plastic wrap between her face and Ned's.

 _There's always a workaround,_ Logan thought, almost cheerful. Marie gave him a shy smile as they walked out the door, and slipped her free hand into his. It was cold and snowy out, and nobody looked twice at a couple holding gloved hands.


	4. Chapter 4

**Summary for the Chapter:**

> [Linguistics] A word formed from another by derivation, such as electricity from electric.

When Pepper descends the steps to Tony's lair of mad science, prepared to drag him away from his latest project, by the hair if necessary, long enough to ingest something with more nutritional content than overbrewed coffee and Red Bull, she hears him chattering excitedly with an unfamiliar voice and immediately knows something is off. "Jarvis," she snaps. "Why didn't you inform me that we had intruders?"

"Intruders is such an unpleasant word," the AI objects mellifluously. Pepper frowns. Jarvis sounds a bit off, too. Almost... moony.

"Your breakfast, Mr. Stark," Pepper announces, sweeping into the lab with an air of unperturbed competence. She'll give whoever else is there five minutes to explain their presence. Then she's calling the Air Force. "Would you like me to have something prepared for your guests?"

"Miss Potts!" Tony cries, delighted, since he knows that she isn't there to haul him off to a meeting. "I'd like to introduce my friend here, Doctor... what was it again?" he asks, turning to one of his visitors, a tall man with dark hair, a pinstriped suit, and converses. Pepper always notices shoes; they tell you a lot about a person. His friend, a beautiful black woman, is wearing very nice boots - a bit of a heel, for vanity, but not so high she can't run. Pepper would bet they both do a fair bit of running.

"Just 'Doctor,'" the man says. He has a British accent to go aong with the suit. Pepper manages to refrain from visibly melting. She's a sucker for accents. So's Tony. Sometimes she wonders if that's why Tony programmed Jarvis to be British, but it's a petty, irrational suspicion and she tries to ignore it. "And this is my companion, Martha Jones."

"It's a pleasure," Pepper says politely, putting down the tray with Tony's breakfast to shake hands. "I'm Pepper Potts, Mr. Stark's assistant."

"Lovely, lovely," the Doctor says, beaming. "We're terribly sorry to intrude, but I'm afraid my vehicle has been experiencing some technical difficulties and this is the only place I could find with the tools to fix it. But I'll be out of your hair in a jiff!"

Pepper looks around for a stealth jet, helicopter, or the Batmobile, but the only unfamiliar item in Tony's workshop is what looks like an old telephone booth. It's blue, and reads _Police Call Box_ across the top. There's a cable running under the door to one of the many wall consoles in the lab. "I've hooked it up to Jarvis with an ethernet cord," Tony explains, seeing her looking. "He'll run a diagnostic and see what's bothering her. Have you tried," he starts, turning to the Doctor, and launches into a stream of technobabble so incomprehensible it makes Pepper's head hurt.

Martha Jones, who hasn't said a word so far, is watching Tony and the Doctor jabber back and forth with an indulgent smile. Pepper suspects she's wearing one to match it. She catches the other woman's eye and jerks her head toward the door. "They'll be at that for a while," she says, once they're outside. "Would you like to go somewhere else while they're busy?"

"Sure." Martha grimaces suddenly. "Only we've been traveling for ages and I've actually got no clue where we are right now."

"California," Pepper replies promptly. "Have you ever been to Rodeo Drive?"

"No. What's that, some kind of cowboy show?"

Pepper grins. "Much better. I'll call Tony's driver. We're going shoe-shopping."

*

Several hours later, Pepper and Martha have ended up at a bar, trading horror stories about life as a companion to a superhero and a time-traveling alien, respectively. The spoils of their shopping campaign are already piled in Happy's limo (Pepper has no doubt that Manolo Blahnik and Salvatore Ferragamo appreciate Stark Industries' tribute to the future hideous disfigurement of their feet), so they're just killing time until whatever crisis inevitably pops up has been dealt with. Pepper gave Jarvis firm instructions not to let Tony or the Doctor out of the house before she got back, but she has few illusions about how well that's likely to work.

"It's just," Martha says, waving around her appletini, "I feel like I'm never the one he wants around, you know? Like, he needs somebody, so there I am, but it's not me he wants there with him."

"Half the time I think Tony just keeps me around because he needs a mother substitute," Pepper offers morbidly, glaring into the bottom of her Sex on the Beach. It's too sweet, and she kind of wants a whisky and soda, but she only started drinking them after she went to work for Tony. Having one while she's bitching about him would feel like hypocrisy.

"You're not anyones substitute, Pepper Potts," Martha says firmly. "Believe me, I'd know."

Pepper would say something reassuring and probably untrue, except that Tony calls at that very moment to tell her that he and the Doctor fixed the "Tardis" (which she infers is the name of the Doctor's phone-box-slash-time-machine) and broken up an intergalactic prostitution ring (which she ignores for the sake of her sanity), and could she bring back Martha Jones as the Doctor is a bit antsy to leave.

*

The Doctor and Tony are still deep in a conversation conducted exclusively in technical jargon when the girls return, and barely even look up. Pepper takes the opportunity to size up the Doctor next to Tony. This man, she thinks, remembering Martha's bits and pieces of stories, Martha's brilliant, beloved, insensitive Doctor, is what Tony could become, given all of eternity to discover how awful people can be. Pepper never thought she would be grateful for Tony's mortality, but she is. One lifetime's worth of betrayal and loss is enough for anyone.

"Well, back to the exciting life of not being Rose Tyler," Martha murmurs in Pepper's ear as they hug goodbye.

"If you ever decide you're tired of time travel and want to settle down with a seven-figure salary, come see me," Pepper says. "I could use someone else around I trust to look after Tony."

"Maybe someday." Martha smiles wistfully. "If you want to come with us..."

"You know I can't leave him," Pepper replies, and it's not a wrench at all.

"Yeah, well, worth a shot," Martha says with a grin, and adds as she steps inside the blue phone box, "Thanks for the shoes!"

"Did you girls have a nice day?" Tony asks absently as they watch the Tardis fade away with a sound like an ancient engine wheezing its way to life.

"Yes," Pepper says.

"That's good." And that's the end of that, at least until the next week, when Pepper discovers Tony's new project.

"Tony, are these schematics for a _time machine_?" She doesn't even wait for his pathetic attempt at a denial. "Absolutely not! Put those away this instant!"

"Jarvis is lonely!" Tony protests, which is true. He's been sulking ever since Martha and the Doctor left. "He misses the Tardis!"

"So build him a friend," Pepper suggests through gritted teeth. "Or spend more time with him. Or buy him a goddamn puppy." She pushes Tony out of the way and begins the long, laborious process of deleting the files from the computer. She can't actually get rid of them completely - only Tony has that kind of sysadmin privileges - but she can make it harder to access them, and it's a good way to register her disapproval. "I don't want you messing around with time, Tony. I have enough to worry about with you playing catch with intercontinental ballistic missiles without adding the possibility that you might get stuck in the Spanish Inquisition or something." She gives Tony a Look, to make sure he's listening, and is slightly taken aback, because Tony is looking at her, too. Maybe Pepper is finally seeing what Martha saw to make her say that Pepper wasn't anyone's replacement, because the expression on Tony's face suddenly seems less like amused condescension, and more... well, affectionate. Maybe even besotted.

"As you wish, Miss Potts," Tony says, leaning over her shoulder to key in the code that will permanently delete the files for the time machine. "As you wish."


End file.
